Method for preparing aromatic sustainable aviation kerosene from biogas

Abstract

The invention discloses a method for preparing aviation kerosene (aromatic hydrocarbon components) from biogas. The method comprises the following steps: separating biogas to obtain methane and carbon dioxide, and then carrying out a two-step chemical reaction process. The method comprises the following steps: firstly, carrying out dehydrogenation aromatization on methane to obtain aromatic hydrocarbon mainly containing benzene and hydrogen, and separating methane for circulating dehydrogenation aromatization reaction; then hydrogen and aromatic hydrocarbon are merged into carbon dioxide, and the polysubstituted aromatic hydrocarbon is obtained by coupling methanol synthesis and alkylation reaction of benzene without external source hydrogen. The method provided by the invention avoids the problem of low selectivity of aviation kerosene fraction hydrocarbons in a route of Fischer-Tropsch synthesis after methane and carbon dioxide are converted into synthesis gas. According to the conversion method for highly coupling the reaction processes, a new route for producing sustainable aviation kerosene from biogas is developed.

Description

Technical Field

[0001] The present application belongs to the field of chemical process development, and specifically relates to the design of reaction routes from biogas to sustainable aviation fuel and the development of corresponding catalysts. Background Art

[0002] Aviation kerosene generally refers to fuel with carbon atoms between C8-C 16 The mixed hydrocarbons between are an indispensable fuel in modern transportation. Jet fuel is currently heavily dependent on fossil fuels, and the aviation industry accounts for about 2-3% of global carbon dioxide emissions. With the growth of aviation demand, this proportion is expected to continue to increase. As an environmentally friendly alternative fuel, sustainable jet fuel (SAF) uses renewable resources as raw materials, which can significantly reduce carbon emissions throughout the life cycle. Jet fuel (CN117229804A) can be produced by isomerization of oil and fat raw materials such as vegetable oil, animal fat, and waste cooking oil after hydrodeoxygenation; Jet fuel can also be obtained by refining green synthesis gas through Fischer-Tropsch synthesis, where green synthesis gas refers to synthesis gas obtained by high-temperature gasification of biomass resources, or capturing carbon dioxide in the air, combining with green hydrogen obtained by electrolysis of water with renewable electricity, and obtaining synthesis gas through reverse water-gas shift reaction.

[0003] In the route using oils and fats as raw materials, the carbon chain length of the hydrocarbons obtained after deoxygenation is C 15 -C 18 (CN105670679B, CN105567284B and CN105567285B), in order to meet the requirements of aviation kerosene properties, subsequent hydrocracking and isomerization treatments have to be carried out. These CC bond breaking processes inevitably form C1-C7 non-aviation kerosene components, resulting in a low yield of the target product. The route of preparing aviation kerosene from syngas by Fischer-Tropsch reaction is limited by Anderson-Schulz-Flory (ASF) distribution, which means that the theoretical selectivity of aviation kerosene is less than 40% (CN117732502A). On the other hand, the products obtained by these routes are all paraffins, lacking the aromatic components necessary for aviation kerosene.

[0004] Biogas is a mixed gas generated by microbial fermentation of organic matter such as kitchen waste, agricultural and forestry waste, and livestock manure under anaerobic conditions. It is a highly carbon-negative C1 raw material, with methane (CH4) and carbon dioxide (CO2) as the main components (50-80% methane, 20-40% carbon dioxide), as well as a small amount of nitrogen and hydrogen, and trace amounts of oxygen and hydrogen sulfide. The sustainable aviation kerosene preparation process route invented by this patent abandons the idea of ​​converting biogas into synthesis gas and then Fischer-Tropsch synthesis, but adopts a new idea of ​​converting methane and carbon dioxide separately and then combining them. The three-step chemical reaction of the present invention is a highly selective process, thereby efficiently converting the carbon in biogas into aromatic components of aviation kerosene. Summary of the invention

[0005] The process route for preparing sustainable aviation kerosene aromatic components from biogas proposed in the present invention generally includes a one-step separation process and a two-step chemical reaction process, and with the catalysts of the corresponding processes, polysubstituted aromatics are finally obtained as aviation kerosene components.

[0006] 1. A method for preparing sustainable aviation kerosene using biogas as raw material, characterized in that the biogas is subjected to a one-step separation process and a two-step chemical reaction process to obtain the aromatic components required for aviation kerosene, comprising the following steps:

[0007] (1) Separation of methane and carbon dioxide in biogas;

[0008] (2) subjecting the methane obtained in step 1 to a dehydrogenation aromatization reaction to obtain aromatic products mainly including benzene and hydrogen; (3) subjecting the carbon dioxide obtained in step 1 to a hydrogenation reaction with the hydrogen obtained in step 2 to obtain methanol, and at the same time, subjecting the aromatics obtained in step 2 to an alkylation reaction with methanol to obtain polysubstituted aromatics.

[0009] 2. The biogas separation method of the present invention is characterized in that solid adsorbent is used for adsorption separation, preferably calcium oxide-based adsorbent is used for adsorption separation;

[0010] 3. The calcium oxide-based adsorbent of the present invention is characterized in that it selectively adsorbs carbon dioxide but does not adsorb other components in biogas such as methane and nitrogen.

[0011] 4. The biogas separation method is characterized in that when a calcium oxide-based adsorbent is selected for adsorption separation, the adsorption bed is selected as a fixed bed or a fluidized bed, preferably a fixed bed.

[0012] 5. The biogas separation method is characterized in that it adopts pressure swing adsorption, and the operating temperature is 600-900°C, preferably 700-800°C; the first stage is the adsorption of carbon dioxide in the biogas, and the adsorption pressure is 0.01-2MPa, preferably 0.1-0.5MPa; after adsorption saturation, it enters the second stage, and the carbon dioxide is decomposed by vacuuming, and the decomposed carbon dioxide is compressed to 2-6MPa after heat exchange cooling, and used as the raw material for the subsequent methanol synthesis reaction.

[0013] 6. The biogas separation method is characterized by using two identical fixed beds. When fixed bed A is in the adsorption stage, fixed bed B is in the desorption stage; after the desorption of fixed bed B is completed, it switches to the adsorption stage, and fixed bed A enters the desorption stage at the same time. Fixed beds A and B cycle the adsorption and desorption operations in turn, so that the separation process is continuous.

[0014] 7. The calcium oxide-based adsorbent is characterized in that it is prepared by a sol-gel method, and the specific process is: according to the content of the required metal oxide, the amount of metal salt theoretically required is calculated to prepare a metal salt aqueous solution, the metal salt is selected from: one or more of nitrates, hydrochlorides, sulfates, citrates, oxalates, and acetates; the cations of the metal salts include one or more of magnesium, aluminum, manganese, zirconium, iron, cobalt, nickel, and copper ions in addition to calcium ions; citric acid and urea are added to the prepared solution, stirred at 20-80°C to form a gel, dried at 80-120°C, and calcined at 400-800°C to obtain the calcium oxide-based adsorbent.

[0015] 8. The methane dehydrogenation aromatization reaction of the present invention is characterized in that a fixed bed reactor is used, and the adsorbed tail gas methane separated from the biogas is directly introduced into the reactor; the reaction temperature is 600-800°C, the reaction pressure is 0.01-2MPa, preferably 0.1MPa; the feed gas space velocity is 500-10000m1·g -1 ·h -1 , preferably 1000-2000ml·g -1 ·h -1 .

[0016] 9. The methane dehydrogenation aromatization reaction is characterized in that the reaction product is separated to obtain liquid aromatics, hydrogen and unreacted methane. Methane is used as circulating gas to continue the dehydrogenation aromatization reaction, liquid aromatics are directly used as raw materials for subsequent alkylation reactions, and hydrogen is compressed to 2-6 MPa as raw materials for subsequent methanol synthesis reactions.

[0017] 10. The methane dehydrogenation aromatization reaction is characterized by the regeneration of the catalyst in the fixed bed. The regeneration process uses oxygen or a mixture of oxygen and carbon dioxide as an oxidant, the regeneration temperature is controlled at 500-800°C, and the regeneration tail gas contains carbon monoxide and carbon dioxide, which are combined with the carbon dioxide separated from the biogas and used as a raw material for methanol synthesis.

[0018] 11. The catalyst for the methane dehydrogenation aromatization reaction is characterized by comprising oxides, nitrides or phosphides of metals such as molybdenum, tungsten, iron, gallium, rhenium, and molecular sieve carriers such as ZSM-5 and MCM-22.

[0019] 12. The methanol synthesis reaction of the present invention is characterized in that a fixed bed reactor is used to introduce the carbon dioxide analyzed in step (1), the carbon monoxide and carbon dioxide regenerated in step (2), and the hydrogen obtained in step (2) to carry out the methanol synthesis reaction.

[0020] 13. The methanol synthesis reaction is characterized in that the reaction temperature is 200-400°C, the reaction pressure is 1-10MPa, preferably 4-6MPa; the reaction space velocity is 100-10000ml·g- 1 ·h- 1 , preferably 300-1000ml·g -1 ·h -1 .

[0021] 14. The alkylation reaction of the present invention is characterized in that the same reactor is used for methanol synthesis, and the methanol generated in situ by hydrogenation of carbon dioxide is used to carry out alkylation reaction with the aromatic hydrocarbons obtained in step (2).

[0022] 15. The alkylation reaction is characterized in that the reaction temperature and pressure are the same as those of methanol synthesis, the reaction temperature is 200-400°C, the reaction pressure is preferably 4-6MPa, and the unreacted methanol is recycled.

[0023] 16. The alkylation reaction is characterized in that the reaction product contains polymethyl substituted benzene with 2 to 6 methyl groups and a carbon number distribution range of C8-C 12 , the content falling within the aviation fuel range is greater than 90%.

[0024] 17. The methanol synthesis catalyst of the present invention is characterized in that it contains one or more oxides or composite oxides of metallic iron, copper, zinc, aluminum, zirconium, gallium, indium, and chromium.

[0025] 18. The catalyst for the alkylation reaction is characterized by having abundant external surface acid sites, and comprises molecular sieves such as HZSM-5, HBeta, HY, as well as aluminum oxide, amorphous silicon aluminum oxide, etc.

[0026] 19. The methanol synthesis coupled alkylation reaction of the present invention is characterized in that the catalyst can be loaded in such a way that the two catalysts are physically mixed and then loaded, or the upper layer is loaded with the methanol synthesis catalyst and the lower layer is loaded with the alkylation reaction catalyst.

[0027] 20. The present invention has the following characteristics:

[0028] (1) The methane and carbon dioxide in the biogas are separated and converted separately, and each step is a highly selective reaction;

[0029] (2) The main aromatic rings in the final product come from methane dehydrogenation aromatization;

[0030] (3) The hydrogen required for carbon dioxide hydrogenation comes from the methane dehydrogenation aromatization reaction, and no external hydrogen is required;

[0031] (4) Methanol, the product of carbon dioxide hydrogenation, is used as an alkylating agent to polyalkylate the benzene rings obtained by dehydrogenation and aromatization of methane, so that the carbon number of the product falls within the range of jet fuel;

[0032] (5) The hydrogenation of carbon dioxide to produce methanol and the alkylation reaction are coupled in one reactor, saving the number of devices;

[0033] (6) The present invention converts biogas into sustainable aviation fuel, which helps reduce the aviation industry's dependence on fossil energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Reaction process for preparing sustainable aviation fuel (containing polysubstituted aromatics) using biogas as raw material DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described below in conjunction with the specific embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0036] Example

[0037] Example 1

[0038] The present invention discloses a method for preparing aviation kerosene (aromatic components) from biogas (see Figure 1 ). The process of the method is as follows: biogas is separated to obtain methane and carbon dioxide, and then a two-step chemical reaction process is carried out. First, methane is dehydrogenated and aromatized to obtain aromatic hydrocarbons and hydrogen mainly composed of benzene, and methane is separated for cyclic dehydrogenation and aromatization reaction; then hydrogen and aromatic hydrocarbons are incorporated into carbon dioxide, without the need for exogenous hydrogen, and methanol synthesis and benzene alkylation reactions are coupled to obtain polysubstituted aromatic hydrocarbons. The present invention avoids the problem of low selectivity of hydrocarbons in the aviation kerosene fraction in the route of converting methane and carbon dioxide into synthesis gas and then performing Fischer-Tropsch synthesis. The highly coupled conversion method used in the present invention has opened up a new route for producing sustainable aviation kerosene from biogas.

[0039] 1. Separation of biogas into methane and carbon dioxide

[0040] In the biogas separation unit, 10 g of the molded MnMgCaO adsorbent was added to fixed bed A and fixed bed B respectively. The system was purged with nitrogen, and then the two fixed beds were heated to 700 °C under a nitrogen atmosphere. Biogas (components and content are shown in Table 1) was introduced into fixed bed A through valve switching, with a flow rate of 100 ml min -1At this time, the following reaction occurs in the fixed bed A:

[0041] CO2+CaO=CaCO3

[0042] Carbon dioxide is fixed on the adsorbent in the form of calcium carbonate. The tail gas at the outlet of fixed bed A is shown in Table 1. After fixed bed A adsorbs for 30 minutes, the biogas is switched to fixed bed B for adsorption. At the same time, fixed bed A is vacuumed. At this time, the following reactions occur in fixed bed A:

[0043] CaCO3=CaO+CO2

[0044] The vacuum analysis time was set to 30 min. The components and contents of tail gas analyzed by fixed bed A are shown in Table 1. After the analysis of fixed bed A was completed, the valve was switched to introduce biogas to allow it to enter the second round of adsorption, and fixed bed B began to vacuum and analyze carbon dioxide. Fixed beds A and B were operated in a reciprocating cycle of adsorption and analysis.

[0045] Table 1. Gas composition table

[0046]

[0047] As can be seen from Table 1, the adsorption separation process achieves the separation of biogas into two gases, mainly methane (content greater than 90.0%) and carbon dioxide (content greater than 95.0%). The adsorption tail gas and the analytical tail gas are compressed by a booster pump and stored in a buffer tank, and they will be used in the next conversion process.

[0048] 2. Methane dehydrogenation aromatization reaction

[0049] The methane dehydrogenation aromatization reaction was carried out in a fixed bed reactor. 10.0 g of the formed Mo / HZSM-5 catalyst was loaded into the fixed bed, and after replacing with nitrogen, the reactor temperature was raised to 700 °C. Then the gas was switched to the buffered adsorbed tail gas (mainly methane), and the flow rate was set to 200 ml min -1 At this time, the main methane dehydrogenation aromatization reaction occurs in the fixed bed:

[0050] 6CH4=C6H6+9H2

[0051] The generated benzene is liquefied by cooling the reaction products, thereby separating it from the reaction products. The remaining gas can be used to separate hydrogen using PSA and used as circulating gas to continue the methane dehydrogenation aromatization reaction. The hydrogen is pressurized to 4 MPa and stored in a buffer tank for subsequent methanol synthesis.

[0052] After the dehydrogenation aromatization reaction was carried out for 6 hours, the catalyst was regenerated. During regeneration, the reactor temperature was maintained at 700°C, the reaction gas was switched to nitrogen purge, and then switched to a mixture of oxygen and carbon dioxide with an oxygen volume fraction of 1%. At this time, the main carbon deposition elimination reaction occurred in the fixed bed:

[0053] 2C+O2=2CO

[0054] C+O2=CO2

[0055] CO2+C=2CO

[0056] The regenerated tail gas is incorporated into the carbon dioxide analyzed during biogas separation and used together as the raw material for methanol synthesis. The regeneration time is 2 hours. After the regeneration is completed, it is purged with nitrogen, and then the gas is switched to methane to continue the dehydrogenation aromatization reaction. The operation of methane dehydrogenation aromatization and catalyst regeneration is circulated in this way.

[0057] 3. Methanol synthesis and alkylation of benzene

[0058] Methanol synthesis and benzene alkylation reactions were carried out in the same fixed bed reactor. 1.0 g of molded methanol synthesis catalyst CuZnZrO x After uniformly mixing with 1.0g of the molded alkylation catalyst HZSM-5, it was loaded into the reactor. After nitrogen replacement, the catalyst was pretreated with a hydrogen-nitrogen mixed gas with a hydrogen gas volume fraction of 10%, the treatment temperature was 240°C, and the treatment time was 4h. After the treatment was completed, the hydrogen-nitrogen mixed gas was turned off, and the carbon dioxide and hydrogen in the buffer tank were introduced, and the carbon dioxide flow rate was set to 10ml·min -1 , the hydrogen flow rate was set to 30 ml min -1 , raise the fixed bed temperature to 350°C, control the reaction system pressure to 4 MPa, and then pump in benzene with a flow rate of 0.001 ml min -1 , the coupling reaction of benzene alkylation and methanol synthesis began. After 24 hours of reaction, the organic liquid sample was taken for analysis, and the results are shown in Table 2.

[0059] Table 2 Analysis of liquid organic products from the alkylation reaction of methanol synthesis coupled with benzene

[0060]

Claims

1. A method for preparing sustainable aviation kerosene using biogas as raw material, characterized in that: Biogas is separated into one step and then reacted in two steps to obtain the aromatic components required for sustainable aviation fuel, including the following steps: (1) Separation of methane and carbon dioxide in biogas; (2) subjecting the methane obtained in step 1 to a dehydrogenation aromatization reaction to obtain aromatic products mainly composed of benzene and hydrogen; (3) The carbon dioxide obtained in step 1 is subjected to a hydrogenation reaction with the hydrogen obtained in step 2 to obtain methanol, and the aromatic hydrocarbons obtained in step 2 are subjected to an alkylation reaction with methanol to obtain polysubstituted aromatic hydrocarbons.

2. The method according to claim 1, characterized in that The adsorptive separation is carried out using a solid adsorbent, preferably a calcium oxide based adsorbent.

3. The method according to claim 2, characterized in that: Calcium oxide-based adsorbents selectively adsorb carbon dioxide, but do not adsorb other components in biogas such as methane and nitrogen.

4. The method according to claim 2, characterized in that: When calcium oxide-based adsorbent is used for biogas separation for adsorption separation, a fixed bed or a fluidized bed is selected as the adsorption bed, and a fixed bed is preferred.

5. The method according to claim 4, characterized in that: Biogas separation adopts pressure swing adsorption, and the operating temperature is 600-900℃, preferably 700-800℃; the first stage is the adsorption of carbon dioxide in biogas, and the adsorption pressure is 0.01-2MPa, preferably 0.1-0.5MPa; after adsorption saturation, it enters the second stage, and the carbon dioxide is decomposed by vacuum pumping. The decomposed carbon dioxide is compressed to 2-6MPa after heat exchange cooling and used as the raw material for the subsequent methanol synthesis reaction.

6. The method according to claim 2, characterized in that: Two identical fixed beds are used for biogas separation. When fixed bed A is in the adsorption stage, fixed bed B is in the decomposition stage. After the decomposition of fixed bed B is completed, it switches to the adsorption stage, and fixed bed A enters the decomposition stage at the same time. Fixed beds A and B cycle the adsorption and decomposition operations in turn, making the separation process continuous.

7. The method according to claim 2, characterized in that: The calcium oxide-based adsorbent is prepared by a sol-gel method, and the specific process is: according to the content of the required metal oxide, the amount of the theoretically required metal salt is calculated to prepare a metal salt aqueous solution, wherein the metal salt is selected from: one or more of nitrates, hydrochlorides, sulfates, citrates, oxalates, and acetates; the cations of the metal salts include one or more of magnesium, aluminum, manganese, zirconium, iron, cobalt, nickel, and copper ions in addition to calcium ions; citric acid and urea are added to the prepared solution, stirred at 20-80°C to form a gel, dried at 80-120°C, and calcined at 400-800°C to obtain the calcium oxide-based adsorbent.

8. The method according to claim 1, characterized in that: The methane dehydrogenation aromatization reaction uses a fixed bed reactor, and the adsorbed tail gas methane separated from the biogas is directly introduced into the reactor; the reaction temperature is 600-800℃, the reaction pressure is 0.01-2MPa, preferably 0.1MPa; the feed gas space velocity is 500-10000ml·g -1 ·h -1 , preferably 1000-2000ml·g -1 ·h -1 .

9. The method according to claim 1, characterized in that: The methane dehydrogenation aromatization reaction separates the reaction products to obtain liquid aromatics, hydrogen and unreacted methane. Methane is used as circulating gas to continue the dehydrogenation aromatization reaction. Liquid aromatics are directly used as the raw material for the subsequent alkylation reaction. Hydrogen is compressed to 2-6MPa as the raw material for the subsequent methanol synthesis reaction.

10. The method according to claim 1, characterized in that: The methane dehydrogenation aromatization reaction requires regeneration of the catalyst in the fixed bed. The regeneration process uses oxygen or a mixture of oxygen and carbon dioxide as an oxidant. The regeneration temperature is controlled at 500-800°C. The regenerated tail gas contains carbon monoxide and carbon dioxide, which are incorporated into the carbon dioxide separated from the biogas and used as a raw material for methanol synthesis.

11. The method according to claim 1, characterized in that: The catalyst for the methane dehydrogenation aromatization reaction includes oxides, nitrides or phosphides of metals such as molybdenum, tungsten, iron, gallium, rhenium, and molecular sieve carriers such as ZSM-5 and MCM-22.

12. The method according to claim 1, characterized in that: The methanol synthesis reaction uses a fixed bed reactor, and uses the carbon dioxide analyzed in step (1), the carbon monoxide and carbon dioxide regenerated in step (2), and the hydrogen obtained in step (2) as raw materials to carry out the methanol synthesis reaction.

13. The method according to claim 1, characterized in that: Methanol synthesis reaction temperature 200-400 ° C, reaction pressure 1-10MPa, preferably 4-6MPa; reaction space velocity 100-10000ml g -1 ·h -1 , preferably 300-1000ml·g -1 ·h -1 .

14. The method according to claim 1, characterized in that: The alkylation reaction and methanol synthesis use the same reactor to carry out an alkylation reaction on the aromatic hydrocarbons obtained in step (2) and the methanol obtained in step (3).

15. The method according to claim 1, characterized in that: The alkylation reaction has the same reaction temperature and pressure as the methanol synthesis, the reaction temperature is 200-400°C, preferably 400°C; the reaction pressure is preferably 4-6MPa, and the unreacted methanol is recycled.

16. The method according to claim 1, characterized in that: The alkylation reaction product is mainly polymethyl substituted benzene, the number of methyl groups is 2-6, and the carbon number distribution range of the product is C8-C 12 .

17. The method according to claim 1, characterized in that: The methanol synthesis catalyst comprises one or more oxides or composite oxides of metal iron, copper, zinc, aluminum, zirconium, gallium, indium, and chromium.

18. The method according to claim 1, characterized in that: The catalysts for the alkylation reaction have abundant external surface acidic sites, including molecular sieves such as HZSM-5, HBeta, HY, as well as alumina, amorphous silica-alumina, etc.

19. The method according to claim 1, characterized in that: The loading method of the methanol synthesis coupled alkylation reaction catalyst is that the two catalysts can be loaded after being physically mixed, or the methanol synthesis catalyst can be loaded on the upper layer and the alkylation reaction catalyst can be loaded on the lower layer.

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